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ANATOMY AND PHYSIOLOGY 
or have been less carefully investigated, for a com- 
paratively limited number of insects are mentioned 
as possessing them. Among these are the carni- 
vorous Coleoptera, Dytiscidas, Silphidse, certain Bra- 
chelytrous species, a few Diptera, &c. Notwith- 
standing their occasional complexity, we can for the 
most part discern without difficulty an apparatus for 
secretion, one or more deferential canals, and a re- 
servatory bag emitting an excretory conduit which 
empties itself into the rectum, just above the anus. 
The fluids secreted are commonly colourless, and 
highly caustic and odorous. These properties may 
be easily determined by taking one of the largei 
Carabi and handling it roughly, when it will probably 
discharge the fluid, which it does with considerable 
force in sudden jets, and if it fall on the skin, it pro- 
duces a sharp burning sensation, which however is 
very transient. In Carabus auratus the vessels in 
question consist of two branches of globular bodies, 
one on each side, resting on a footstalk, connected 
with a long deferential canal, opening into a large 
ovoid bladder. Chlcenius velutinus (PL II. fig. 7, a, a,) 
has the secreting vesicles disposed on the tops of 
small branchlets, so that the whole apparatus looks 
not unlike a branch of a willow covered with catkins. 
In the same fig. b is the deferential canal ; c, d, the 
bladder. Fig. 8 in the same plate, represents these 
parts as they appear in the Bombardiers , a kind of 
beetles which have been long famous for possessing 
the power of producing an explosion accompanied 
with a discharge of smoke. This is caused by the 
